1. Field of the Invention
This application relates to a system for utilizing solar power to drive a free-piston Stirling engine, and in particular a Stirling engine primarily designed for that application.
2. Description of the Prior Art
One of the most sought after goals in the field of energy conversion is the efficient transfer of solar energy to other usable forms of energy, such as heat energy, mechanical energy and electrical energy. To some extent such efforts have been successful, but only in limited applications, such as the heating of water, passive space heating, and the like. To date, the efficient conversion of solar energy into electrical energy has eluded those working on the problem. The conversion of solar energy to electrical energy has only been accomplished on a very small scale, or in situations where cost effectiveness is not a primary consideration, such as the power of satellite experiments.
In an area of technology hitherto unrelated to solar energy conversion, work has been done on the development of Stirling engines. Stirling engines require a heat source, typically provided by fossil fuel combustion. On paper, at least, the Stirling engine makes very efficient use of heat energy, and it is an attractive alternative to other heat energy devices, such as the internal combustion engine. However, in practice Stirling engines have been unable to achieve their theoretical efficiency.
Several Stirling cycle free piston machines are described in my U.S. Pat. No. 4,044,558 all of which function as resonant thermomechanical oscillators in which the oscillating elements harmonically oscillate at resonant frequency but at a controlled phase difference. In this former patent the resonant frequency is tuned by varying the volume of at least one gas spring chamber and the phase angle between oscillating elements is varied by varying the dead volumes of the gas spring chambers which may be filled with a matrix to cause the compression and expansion of the gas spring fluid to be isothermal processes so as to minimize the gas spring hysteresis losses.